1. Field of the Invention
The present invention relates to a liquid-jet head and a liquid-jet apparatus, and particularly relates to an ink-jet recording head and an ink-jet recording device where: a part of each pressure generating chamber communicating with a nozzle orifice for ejecting ink droplets is formed of a vibration plate; a piezoelectric element is provided on a surface of the vibration plate; and the ink droplets are ejected by displacement of the piezoelectric element.
2. Background Art
There have been two types in practical use as an ink-jet recording head where: a part of each pressure generating chamber communicating with a nozzle orifice for ejecting ink droplets includes a vibration plate; and ink droplets are ejected through the nozzle orifice in a manner that a pressure is applied onto ink in the pressure generating chamber by causing a piezoelectric element to deform the vibration plate. One of these two types is a head using piezoelectric actuators of a longitudinal vibration mode in which the piezoelectric actuators are elongated and contracted in an axial direction of piezoelectric elements. Another one uses piezoelectric actuators of a flexure-vibration mode. In the case of the former type, it is possible to produce a head suitable for high-density printing since end faces of piezoelectric elements make contact with a vibration plate and a volume of each pressure generating chamber is changed, but on the other hand, there is a problem that manufacturing processes are complicated. In this type, a method of cutting and separating the piezoelectric elements into comb-teeth like shapes so as to correspond to arrangement pitches of nozzle orifices, is required. Moreover, an operation of positioning the cut and separated piezoelectric elements in order to attach them to the pressure generating chambers to fix them. Contrastively, in the case of the latter type, it is possible to have piezoelectric elements formed on a vibration plate in a relatively easy process, where a green sheet which is provided as a material for the piezoelectric elements is attached in accordance with shapes of pressure generating chambers, and is baked thereafter. However, there is a problem that a high-density arrangement is difficult because this type requires an area large enough to allow utilization of flexure vibrations.
For the purpose of resolving the above described disadvantage in the latter type of recording head, there is another type of recording head where piezoelectric elements are formed so as to be independent from each other in a manner corresponding respectively to pressure generating chambers. In this manner, the piezoelectric elements are formed by forming a uniform piezoelectric material layer on an entire surface of a vibration plate with a deposition technique, and then, through a lithography technique, piezoelectric material layer is cut and separated into shapes corresponding to the respective pressure generating chambers. According to this type, the process of attaching the piezoelectric elements to the vibration plate is not required. The piezoelectric elements can be formed in a high-density state by using the precise and convenient lithography technique, and also, there is an advantage that a thickness of the piezoelectric elements can be thinner and thereby a high-speed drive is possible.
However, in an ink-jet recording head where piezoelectric elements are thus arranged in a high-density state, there are following problems since one electrode (a common electrode) of each of the piezoelectric elements is provided to be shared by the plural piezoelectric elements. When a large number of the piezoelectric elements are simultaneously driven to eject a large amount of ink droplets, ink ejection characteristics are deteriorated because a voltage drop occurs and displacements of the piezoelectric elements comes to be unstable. Note that, particularly with respect to an electrode of a piezoelectric element formed of a thin film, the electrode has-a relatively high resistance value because the film is thin, and hence is more likely to bring about the aforementioned problem.
For the purpose of solving these problems, there is a technology where a resistance value of the common electrode is substantially reduced by providing a connection wiring layer in a region facing a vicinity of an edge portion of each piezoelectric element in a longitudinal direction of the piezoelectric element. The connection wiring layer is electrically connected to the common electrode of the piezoelectric elements (for example, refer to Japanese Patent Application publication No. 2004-1431).
In order to reduce the resistance value of the common electrode, the connection wiring layer is made of a material which has relatively high conductivity, for example, a metal material such as gold (Au) or Aluminum (Al). Additionally, the connection wiring layer is formed to have a thickness substantially equal to that of the vibration plate, for example, between 1 and 3 μm. On the other hand, in many cases, the vibration plate is made of a material which has relatively low conductivity. For example, in Patent Document 1, a vibration plate is disclosed which includes an elastic film made of silicon dioxide (SIO2) formed by thermally oxidizing a passage-forming substrate which is a single crystal silicon substrate.
Additionally, as methods of manufacturing the connection wiring layer, general ones are a spattering method, and a method where a film is patterned through etching after it has been deposited through a vapor deposition technique. In order to obtain a film having good adhesion with an undercoat thereof, through the spattering method or through the evaporation deposition technique, it is necessary to perform deposition while heating the passage-forming substrate (the vibration plate) at a temperature of about 100 to 300° C. Furthermore, in the spattering method, the deposition proceeds while atoms collide with the passage-forming substrate (the vibration plate). Accordingly, even without heating the passage-forming substrate, a temperature of the passage-forming substrate (the vibration plate) comes to be 150 to 300° C.
Therefore, when the connection wiring layer is deposited with the spattering method or the like, there is a problem that a membrane stress remains on the vibration plate, due to a difference in amount of contraction between the vibration plate and the connection wiring layer at a cooling phase. That is, there is a problem that, as the membrane stress remains on the vibration plate, the vibration plate around a periphery of the connection wiring layer easily cracks if en external force is imposed. The external force is, for example, a pressure application when a head is assembled, or capping when the head is used.
Additionally, among ink-jet recording heads of this type, for example, there is one head having a configuration where a reservoir includes a communicating portion and a reservoir portion, and ink is supplied from this reservoir to each pressure generating chamber (for example, refer to Japanese Patent Application publication No. 2004-216581). The communicating portion is provided on a passage-forming substrate, and the reservoir portion is provided on a reservoir forming plate joined to the passage-forming substrate. Here, in the ink-jet recording head having this configuration, there is a case that ink (moisture) in the reservoir infiltrates from the interface between the passage-forming substrate and the reservoir forming plate, and when the ink reaches a connection wiring layer, a voltage is applied to the ink. Accordingly, electrolysis is operated on the ink, and gas and foreign substances are generated, whereby ejection of ink droplets becomes inferior. Furthermore, if the ink reaches a piezoelectric element, there is a possibility that the ink destroys the piezoelectric element. Moreover, particularly in the structure where the connection wiring layer is provided as described above, a problem of this kind is more likely to occur as a thickness of an adhering agent to join the reservoir forming substrate, comes to be relatively large.
Meanwhile, it is obvious that the abovementioned problems are involved not only in ink-jet recording heads which eject ink, but also are involved similarly in other liquid-jet recording heads which eject liquid droplets other than ink.